We hypothesize that acylation is a mechanism of chemical teratogenesis. If acylation is a mechanism of teratogenicity, then acylating agents such as anhydrides (and imides) should be teratogenic. The embryotoxicity and teratogenicity of a variety of anhydrides (acetic, propionic, succinic, maleic, and phthalic) and succinmide were evaluated following intraperitoneal administration of gestations days 8, 9, and 10 or 11, 12, and 13. All the compounds tested were both embryotoxic and teratogenic. The most common congenital abnormalities induced by treatment on days 8, 9, and 10 were rib and vertebral malformations. Treatment on gestational days 11, 12, and 13 produced predominantly cleft palate. In vivo studies indicated that phthalic anhydride was bound to macromolecules of maternal liver, lung, kidney, and spleen as well as the uterus, placenta and fetuses. These results suggest a correlation of these acylating reagents between their teratogenic potential and their chemicobiological interactions.